This invention relates to the recovery and/or beneficiation of coal from a slurry containing coal in water.
The invention is particularly applicable to the recovery of coal from a slurry pipeline used for transportation of the coal and also to the recovery and beneficiation of coal from a variety of slurries produced in washing and beneficiating operations. Specific examples include intermediate and waste slurries produced from fine coal washing circuits where a considerable amount of valuable coal matter is frequently discharged into ponds and other disposal areas, and also slurries produced by crushing coarse coal washery reject material (such as that rejected from a dense medium cyclone).
In the case of pipeline slurries used for the transportation of coal, the coal is normally dewatered using conventional equipment such as centrifuges or vacuum filters. Whilst these techniques may be suitable for handling coals for power generation at a captive generation station, they are not suitable for handling many coking coals. For coking coals, the presence of clays and other mineral matter can result in a serious deterioration of coking properties of the coal if not removed from the coal in the dewatering operation. (See Rigby, G. R. and Callcott, T. G., "A System for the Transportation, Cleaning and Recovery of Australian Coking Coals", Paper E5, Fifth International Conference on the Hydraulic Transport of Solids in Pipes, Hanover, May 1978 (1)). Conventional dewatering equipment cannot recover coal in this manner without significant loss of fine coal.
The invention involves the application of selective agglomeration techniques to the coal recovery operation. In this technique, the coal matter being hydrophobic can be readily separated from the hydrophilic clays and mineral matter suspended in the slurry by the addition of an appropriate "oil". The "oil" being hydrophobic, collects the coal, and with the appropriate contacting pattern provided by this invention, can be formed into agglomerates which are readily separated from the non-hydrophobic mineral components in the aqueous suspension.
The "oil" used in the operation can consist of a wide variety of liquid hydrocarbons such as kerosene, diesel oil, fuel oil, petroleum residues through to heavy aromatic materials such as coke oven tars and bitumen together with various mixtures.
Emulsification of the oil with water in some cases has been shown to provide more efficient operation (see for example Australian Pat. No. 221,773).
Many publications and patents have discussed the recovery of coal and other carbonaceous material from various slurries using selective agglomeration techniques; for example see:
Lemke, K., "The Cleaning and De-watering of Slurries by the Convertol Process", 2nd Int. Coal Prep. Congr. Essen, Germany, 1974. (2)
Capes, C. E., McIlhinney, A. E. and Coleman, R. D., "Beneficiation and Balling of Coal", Soc. Min. Engrs. AIME, Trans., 247, pp 233-7 (1970). (3)
Swanson, A. R., Nicol, S. K. and Bensley, C. N., "Selective Agglomeration-A Solution to Problems in the Efficient Treatment of Fine Coal", Chemeca 77 Conference,
Canberra, September, 1977. (4)
U.S. Pat. No. 3,856,668. (5)
Zuiderweg, F. J. and Lookeren Campagne, N. van, "Pelletizing of Soot in Waste Water of Oil Gasification Plant-The Shell Pelletizing Separator" (S.P.S.)", Chem. Eng., CE 223-6, July/August 1968. (6) However these techniques have generally involved the use of complex mixing chambers and/or tanks, or other substantial agglomerating devices to achieve the desired degree of beneficiation and agglomeration of the coal so that adequate separation from the liberated mineral matter could be achieved.
It is the object of the present invention to provide a greatly simplified means of achieving separation of coal from coal bearing slurries.